EVOLUTION

Natural Selection

a. Explain why natural selection acts on the phenotype rather than the genotype of an organism The English naturalist, Charles Darwin, formulated the theories to help our understanding of natural selection. There are still widely upheld. His theory can be summed up in that many plants and animals do not survive because nature "weeds out" certain organisms who are unable to adapt to the changing environmental conditions. The strongest and most efficient survive and produce offsprings. Organisms who were able to provide necessary food, shelter, and avoid predators were more successful in reproducing offspring. The less successful types do not pass on as many traits because they have fewer descendants. And, over time, failure to reproduce at a rate equal to or greater than the mortality rate can lead to extinction. Natural selection allows the total number of certain members of a population to decline or become extinct due to environmental pressures, while others increase accordingly. One case study of natural selection involved Kettlewell who observed and conducted experiments on the moths in England. Around 1840, there was the first appearance of a dark colored version of the pepper-colored moth. Around this time, there was also an onset of heavy industrial output in that area that produced black smoke with heavily laden soot. Pepper-colored moths were found all over England and were preyed upon birds. Kettlewell theorized that the birds were preying upon these colored moths that were less camouflaged and thus easier to see by the birds, versus the darker colored moths in the soot covered forests. Kettlewell performed an experiment of releasing an equal number of dark and light-colored moths in a soot-covered forest. When he gathered the tagged moths, he had recaptured mostly dark-colored moths. He concluded that the uneven reproductive rates favored an increase in one type of moth over the others. The darker moths had adapted to the environment, survived, and reproduced. His experiment is an example of how environment changes can determine the characteristics of species.

b. Predict the survival potential of various groups of organisms based on the amount of diversity in their gene poolsGenetic diversity is critical for a species's ability to survive environmental changes. Because an environment will not remain stable, it is important that a population is genetically diverse. A population has to adjust over time if an environmental change occurs. Let's say we have a group of giraffes, some with long necks, some with short necks, and some in the middle. The long-necked giraffes are able to reach leaves all the way up tall tress, the short-necked giraffes can eat the leaves on the shorter tress, and the necked giraffes can munch on the trees in the middle. However, let's say a disaster occurred that removed all of the short tress. The short-necked giraffes are unable to eat as they cannot reach those leaves on the taller trees. The other types of giraffes are still doing fine and their species can continue to thrive. However, if ALL of the giraffes had short necks, then the whole population would not survive. The diversity in the neck sizes allowed the population to survive in a disaster. A greater diversity in a gene pool allows for a greater chance of survival and the ability to adapt to environmental changes.

Evolutionary Patterns

a. Analyze fossil evidence with regard to biological diversity, episodic speciation, and mass extinction Extinction, like natural selection, favors the reproduction of certain species at the expense of less-fit species. Fossil evidence indicates that following a mass extinction, such as the Permian extinction (this was when Pangea formed) or at the end of the Cretaceous period (this was when the dinos ruled the world), a period of growth and genetic variation followed. The extinctions allowed for colonization by the remaining species. We also saw speciation, which allowed new biological species to arise. Fossils of mammals shows as considerable amount of speciation and growth in numbers, mostly likely associated with the acquisition of new territory as well as the loss of dinos as predators/competitors.

b. Analyze the effects of evolutionary patterns on the diversity of organisms (e.g., genetic drift, convergent evolution, punctuated equilibrium, patterns of selection) Genetic drift is a result whereby chance or random events changes a gene pool in a population. A genetic drift can result in geographic or reproductive isolation. Geographic isolation is the result of a species that have been physically separated by land or water. Reproductive isolation is when members of a small population reproduce exclusively among themselves. Because mating within a small population is very close, the frequencies of a mutant gene will increase.

Convergent evolution is the result of organisms, not related, independently evolving similar traits as a result of adapting to a similar environmental conditions or occupy a similar niche. For example, wings of the bat, bird, and pterodactyl all morphed into these wing structures independently.

Punctuated equilibrium: there is a time frame for evolution and Darwin's concept is the idea of gradualism. That evolutionary change is slow and gradual. Punctuation equilibrium is the idea that after long periods of stability, it is punctuated in short periods of time a lot of evolutionary change as a result of some geological or environmental change.

c. Explain the conditions for Hardy-Weinberg equilibrium and why they are unlikely to appear in nature, and solve equations to predict the frequency of genotypes in a populationA population includes all of the members of a species that all live in a particular location. Geneticists are concerned about the factors in population that affect gene frequencies. The gene pool is all of the genes that can be inherited in a population. In a non-evolving population, the allele frequency, genotype frequency, and the phenotype frequency remain in a genetic equilibrium. The random assortment of genes during sexual reproduction does not alter the genetic makeup of the gene pool for that population. This observation was noticed by the German physicist Weinberg and the British mathematician, Hardy. The Hardy-Weinberg principal uses the following algebraic equation to computer the gene frequency in a human population: p2 + 2pq + ﻿﻿q2﻿﻿ = 1The Hardy-Weinberg model states that a population will remain at a genetic equilibrium as long as there is no random mating, there is a large population, no migration, and no mutation. Example and practice: Let's say we have R and r as the dominant and recessive alleles for a trait were RR= red, rr=blue, and Rr= purple. Probability of genotype RR= p x p = p2Probability of genotype Rr=(p x q) + (q x p) = 2pqProbability of genotype rr=﻿﻿r x r= r2﻿﻿

Let's say we have a population of 100. 60 have the RR genotype, 30 have the Rr genotype, and 10 have the rr. The allele and genotype frequency for each allele is calculated by dividing the total population in the number for each genotype:RR= 60/100= .6Rr= 30/100= .3rr= 10/100= .1Using this information, we can predict the frequency of the allele in the first generation of offsprings. You need to determine the total number of alleles that is possible in the first generation. So, in this practice, since each organism has 2 alleles and we have 100 organisms, then the total number of possible alleles of the first generation of offspring would be 200. Then, we examine the possibility of each allele. RR= 2 x 60= 120 + Rr (30) = 150. The frequency of the G allele is 150/200= .75. For the g allele, Gg= 30 + gg (2 x 10 = 20) = 50. The frequency for the g allele is 50/200= .25. In the above equation, the letter p is used to identify the allele frequency for the dominant allele and q for the recessive allele. p + q = 1, so, in our example, .75 + .25 = 1

Here's a video explanation by the wonderful Khan Academy:

Mechanisms for Speciation

a. Distinguish between the accommodation of an individual organism to its environment and the gradual adaptation of a lineage of organisms through genetic change Living organisms may be able to adapt to its environment through non-genetic, behavior adaptations. Living organisms also adapt

b. Describe a scenario that demonstrates the effects of reproductive or geographic isolation on speciationThe environment may change in a way such that it creates an external barrier to reproduction such as a river or a mountain range. A physical separation prohibits the gene migration between populations (allotropic speciation). When this happens, natural selection, mutation, and genetic drive will act to diversify genetically the two populations so that they are no longer able to mate and produce fertile offspring. Geographic isolation provides an opportunity for the formation of new species.

History and Origin of Life

a. Explain the theoretical origins of life on Earth The oldest fossil shows that life on Earth was established around 3.5 billion years ago. For life to begin, we need raw materials to form life's critical molecules: DNA, RNA, and proteins. The building blocks of these substances are amino acids. The first one may have been synthesized from methane and ammonia. Methane and ammonia were abundant in the Earth's primitive atmosphere. Theories on how the gasses could have reorganized into useful molecules include ultraviolet light or lightning. Another idea is that amino acids arrived on earth perhaps by meteorites. Another hypothesis proposes that organic material needed for life came from methane and hydrogen sulfide that comes out of deep-sea hydrothermal vents. Some researchers believe that life may have originated along the ancient beaches, where the waves and tides would have brought various organic materials formed in the Precambrian oceans. Investigators demonstrated how organic molecules could have been formed in the early seas. In the 1950s, Stanley Miller experimented with the chemical composition and temperature of the primitive sea. Using sterile water, he placed methane gas, hydrogen, and ammonia and sealed it off so that nothing would be able to enter or leave this water. He heated the water to a temperature of the early sea. The water/gas mixture was subjected to electric sparks. Miller let this experiment run for about a week and at the end he tested the water and found organic compounds. Carl Sagan duplicated Miller's experiment in 1963 and was able to produce ATP from inorganic matter. As we know, ATP is essential to all living cells. Melvin Calvin demonstrated the polymerization of complex molecules. Sidney Fox produced microspheres, long chain peptides.All of these experiments help to contribute to the theory on the origin of life. The earliest life forms were single-celled organisms known as prokaryotes. Prokaryotes have their genetic material (DNA) not separated from the rest of the cell by a nucleus. Because oxygen was absent from the atmosphere at this time, they engaged in anaerobic metabolism to extract energy from "food". Their food source most likely organic molecules in their surroundings. Eventually, this type of bacteria evolved to use solar energy to synthesize organic compounds. This event was an important turning point in evolution. This was the first time that organisms were able to produce food for themselves and for other organisms.

b. Construct a branching diagram (cladogram) from a variety of data sources illustrating the phylogeny between organisms of currently identified taxonomic groupsCladistic analysis is a method to classify organisms to match their evolutionary history as well as common phylogenetic features.How to construct CladogramsInteractive How to Build A Cladogram